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This thesis reports on investigations on the structure and reactivity of dipeptide-alkali metal complexes, a series of ruthenium bearing catalysts, dysprosium based single molecule magnets and organometallic di-cobalt complexes. A variety of experimental and theoretical methods was used dependent on the problem: collision induced dissociation, hydrogen/deuterium exchange reactions, gas phase reactions with \(D_2\), infrared multiple-photon dissociation and the determination of minimum energy structures, IR absorption spectra, transition states and electronic transitions based on density functional theory.
A case study was carried out to explore the influence of alkali metal ions on the gas phase structure of the dipeptide Carnosine. CID experiments on protonated Carnosine and its alkali metal complexes in an ion trap resulted in different fragment pathways dependent on the size of the alkali metal. The complexation of small ions (\(Li^+\) and \(Na^+\)) promoted the cleavage of bonds in the molecules backbone under CID, while \(Rb^+\)- and \(Cs^+\)-Carnosine complexes underwent the exclusive loss of the alkali metal. CID breakdown curves reflected the different binding behavior of the alkali ions to Carnosine. Gas phase H/D exchange reactions with \(D_2O\) resulted in the exchange of several protons of the protonated dipeptide, while its alkali metal complexes underwent no exchange reactions. DFT derived energetical minimum isomers exhibited only charge solvated tridentate structures, whereas salt bridge as well as charge solvated binding motives are reported in literature on complexes of alkali metal ions and oligopeptides. This study was published in a similar version as a paper in Zeitschrift für Physikalische Chemie.
A combination of the four dipeptides Carnosine, Anserine, GlyHis and HisGly with alkali metal ions was investigated with the help of CID, IR-MPD spectroscopy and H/D exchange reactions with \(ND_3\). The aim of the survey was to elucidate the influence of the methyl-group at the histidine ring, of the peptide sequence and chain length on the binding motives of the alkali ions. The experimental results were compared to DFT derived minimum energetical isomers. A moderate accordance was found for DFT predicted IR absorptions to IR-MPD spectra. A systematic nomenclature was developed reflecting all binding motives of the four dipeptides to alkali ions. Carnosine complexes all alkali metal ions in an uniform motive. DFT derived energetical minimum isomers of the three other dipeptides showed strong conformational changes with increasing size of the alkali ion. The most favored binding motive of all peptides was the tridentate complexation of the alkali ion by a carboxylic and an amidic oxygen atom, while the electron donating nitrogen atom either belongs to the Histidine ring or the amine group. The ability to form hydrogen bonds in a certain binding motive is essential for the preference of the Histidine or amine nitrogen atom as an electron donor. The charge solvated binding motive is the most common within all found isomers. Several structures exhibited hydrogen bonded protons. Those can be interpretated as intermediates between the charge solvated and the salt bridge binding motive. CID breakdown curves of the cationic complexes of the dipeptides with \(K^+\), \(Rb^+\) and \(Cs^+\) resulted in a fair agreement of \(E^{50\%}_{com}\) values with DFT derived Gibbs free binding energies. CID led to multiple fragments of the \(Li^+\) and \(Na^+\) dipeptide complexes and to an insufficient correlation between the \(E^{50\%}_{com}\) values and metal-dipeptide free binding enthalpies. Gas phase H/D exchange reactions of the protonated dipeptides with \(ND_3\) resulted in the exchange of all labile protons with comparable relative partial rate constants. The assumption of coexisting single and double exchange reactions per single collision led to an enhancement in quality of the pseudo first order kinetic fits of the experimental derived data. The \(Li^+\), \(Na^+\) and \(K^+\) complexes of the dipeptides exhibited a reduction in the number of exchanged protons, significantly lower rate constants for H/D exchange and only single exchange reactions.
The complexation of the doubly charged cationic transition metal \(Zn^{2+}\) by deprotonated Carnosine led to crucial conformational changes with respect to the alkali metal complexes. Former DFT calculations on the gas phase structure of \([Carn-H,Zn^{II}]^+\) were now compared to IR-MPD spectra. IR-MPD spectra exhibited several of the DFT predicted IR absorptions while the overall agreement in the position of bands is only partially satisfactory. The complex \([Carn-H,Zn^{II}]^+\) was furthermore used in order to study the band dependent enhancement of fragmentation efficiency by application of a resonant 2-color IR-MPD pump/probe scheme. In literature, it is assumed that the slopes of linear fits to the log-log scale of experimental data (fragmentation efficiency vs. laser pulse energy) correlate to the number of photons needed for fragmentation. No reasonable number of photons for the fragmentation of the molecule was derived with this approach. However, it could be shown that the number of photons of the pump laser needed for fragmentation is reduced by the use of a second IR color. The change of the delay between the pump and probe laser pulse had an influence on the shape of the absorption bands. Irradiation with the probe laser pulse before the pump laser caused a heating of the molecule which resulted in a broadening of bands. No broadening was observed when the probe laser was applied simultaneously or after the pump laser. CID and IR-MPD fragmentation channels differed in their relative abundance. Furthermore, relative abundancies of fragments were specific to the excited vibrational motions. This study provides essential approaches for the further study of the mechanism of resonant 2-color IR-MPD spectroscopy.
Several ruthenium catalysts for transfer hydrogenation reactions were synthesized by L. Ghoochany (research group W. Thiel, TU Kaiserlautern). CID measurements on isotopic labeled species led to the following conclusion about the activation process of the catalyst: a nitrogen-ruthenium bond is broken, the pyrimidine ring of the substituted 2-R-4-(2-pyridinyl)pyrimidine ligand rotates about 160° and a carbon-ruthenium bond is formed under subsequent loss of a HCl (or DCl) molecule. The mass spectrometers CID amplitude was calibrated with a set of “thermometer ions”. CID breakdown curves were used for determination of \(E^{50\%}_{com}\) values of three differently substituted catalysts. Finally, activation energies were estimated by means of the calibration. The resulting activation energies showed a qualitative correlation to DFT derived activation energies. These results are part of a manuscript which was submitted to Chemistry – A European Journal and is currently in the review process. Further studies on this series of transition metal complexes included CID on ligand exchanged species, 1- and 2-color IR-MPD spectroscopy, gas phase reactions with \(D_2\) and DFT based modeling of the reaction coordinate of the \(D_2\) insertion. The exchange of the anionic chlorido ligand in solution led to three complexes with different fragmentation thresholds. CID derived activation amplitudes correspond well to the order predicted by the hard/soft acids/bases (HSAB) concept. 1-color IR-MPD experiments on two complexes showed only a few bands. Resonant 2-color IR-MPD increased the overall fragmentation efficiency and uncovered several dark bands. DFT derived IR absorption spectra correlate well to IR-MPD spectra while some bands are still not observable. Gas phase reactions with \(D_2\) showed an increase of the mass of the activated complex of +4 m/z. This was interpreted in terms of an incorporation of a \(D_2\) molecule under heterolytical cleavage of the \(D_2\) molecule and can be compared to a back reaction of the activation. The reaction coordinate of the \(D_2\) incorporation was modeled with DFT at the B3LYP/cc-pVTZ level of theory and different activation energies were derived dependent on the substituent. Reactions of three differently substituted complexes with \(D_2\) resulted in different relative partial rate constants. The comparison to rate constants derived from transition state theory showed a qualitative but not quantitative correlation to the experimental results. This study contributes to our ongoing work on the assignment and isolation of reaction intermediates in the gas phase.
A series of dysprosium based complexes was synthesized by A. Bhunia (research group P. W. Roesky, KIT) and studied within the collaborative research center SFB/TRR 88 “3MET”. We contributed to this work with ESI-MS, CID and experiments on H/D exchange reactions with \(ND_3\) in the gas phase. Those complexes consist of a central triple-charged dysprosium cation and two identical salen-type ligands which allow for a complexation of up to two transition metals. The monometallic dysprosium complex shows single molecule magnet (SMM) behavior in SQUID measurements, while the incorporation of two double-charged manganese cations leads to ferromagnetic behavior. The interaction of terminal amine groups with the manganese ions caused a hinderance of the exchange H/D exchange reaction with \(ND_3\) in the gas phase. Alternatively, the terminal amine groups of the monometallic dysprosium complex allow for the bond of two \(Ni^{2+}(tren)\) complexes. ESI-MS studies showed anionic as well as cationic complexes due to deprotonation or protonation in solution. CID studies led to fragmentation schemes which correlate quite well to the predicted structures of the complexes. These results are part of two publications in Inorganic Chemistry and Dalton Transactions. Further studies on this series of mono-, di- and trimetallic complexes are reported in this thesis. H/D exchange reactions with \(D_2O\) in solution yielded in an exchange of all labile protons for the cationic complexes. Anionic complexes underwent a partial or a complete exchange of labile protons. A comparison of 1- and 2-color IR-MPD spectra of anionic and cationic complexes as well as H/D exchanged species allowed for the assignment of vibrational bands. Furthermore, preferred protonation sites were derived by comparing the results of IR-MPD experiments and H/D exchange reactions in solution and in the gas phase. This study contributes to our ongoing work on the determination of magnetic properties of isolated ions in the gas phase at the Helmholtz-Zentrum Berlin.
The complex \([(^4CpCo)_2(\mu-C_2Ph_2)]\) (\(^4Cp\) = tetraisopropyl-cyclopentadiene) was synthesized by J. Becker (research group H. Sitzmann, TU Kaiserslautern). The cationic complex and several reaction products were characterized by ESI-MS. Some of the experimental data contributed to the diploma thesis of J. Becker. The cationic reaction products and the complex itself were subject of IR spectroscopic characterization. IR-MPD efficiency changed crucially with modification of the complex, yielding \([(^4CpCo)_2(\mu-C_2Ph_2)X]^+ (X=H, (H+CH_3CN), Cl, O)\). The contribution of various fragmentation channels to the overall fragmentation efficiency was studied in detail. An increase of photon flux resulted in a saturation of preferred \(C_2Ph_2\) loss, additional alkyl fragments out of the \(^4Cp\) rings arising. Several absorption bands were found in the mid- and near-IR region. A model system from literature was used to identify seemingly levels of DFT theory by reference to X-ray crystal structure data. The B3LYP and the B97D functional with cc-pVDZ and Stuttgart 1997 ECP basis sets were identified for calculations of the complex \([(^4CpCo)_2(\mu-C_2Ph_2)]^+\) and of its reaction products. An elongation of the Co-Co bond distance was observed for the cationic reaction products with \(Cl^-\) and \(O^{2-}\). Calculations with B3LYP and B97D resulted in different electronic ground states. We did not obtain a good agreement of calculated vibrational modes and recorded IR-MPD spectra. DFT predicted more absorption bands than observed, especially those corresponding to aliphatic symmetric \(CH_n (n=2, 3)\) and aromatic CH stretch motions. Future 2-color IR-MPD experiments might resolve currently prevailing discrepancies. TD-DFT calculations yielded several electronic transitions that do not correspond to the IR-MPD spectra. The chosen levels of theory for DFT and TD-DFT calculations does not seem to be appropriate. IR-MPD spectra have to be remeasured in order to normalize the spectra to photon flux. Furthermore, a different strategy has to be developed for ab initio calculations on the complexes under study.
A combination of various methods applied to isolated ions in the gas phase and in solution allowed for the study of their structure, binding energies and reactivity. 1- and 2-color IR-MPD spectroscopy combined with DFT predicted absorption spectra of different isomers enabled an assignment of vibrational bands and binding motives of the molecules. The derived results are important for further studies on the binding behavior of peptides and the reaction behavior of metal complexes.

This thesis combined gas phase mass spectrometric investigations of ionic transition metal clusters that are either homogeneous \((Nb_n^{+/-}, Co_n^{+/-})\) or heterogeneous \(([Co_nPt_m]^{+/-})\), of their organo metallic reaction products, and of organic molecules (aspartame and Asp-Phe) and their alkali metal ion adducts.At the Paris FEL facility CLIO a newly installed FT-ICR mass spectrometer has been modified by inclusion of an ion bender that allows for the usage of additional ion sources beyond the installed ESI source. The installation of an LVAP metal cluster source served to produce metal cluster adsorbate complex ions of the type \([Nb_n(C_6H_6)]^{+/-}\). IR-MPD of the complexes \([Nb_n(C_6H_6)]^{+/-} (n = 18, 19)\) resulted in \([Nb_n(C_6)]^{+/-} (n = 18, 19)\) fragments. Spectra are broad, possibly because of vibronic / electronic transitions. In Kaiserslautern the capabilities of the LVAP source were extended by adding a gas pick up unit. Complex gases containing C-H bonds otherwise break within the cluster forming plasma. More stable gases like CO seem to attach at least partially intact. Metal cluster production with argon tagged onto the cluster failed when introducing argon through the pick up source, but succeeded when using argon as expansion gas. A new mass spectrometer concept of an additional multipole collision cell for metal cluster adsorbate formation is currently under construction. Subsequent cooling shall achieve high resolution IR-MPD spectra of transition metal cluster adsorbate complexes.Prior work on reaction of transition metal clusters with benzene was extended by investigating the reaction with benzene and benzene-d6 of size selected cationic cobalt clusters \(Co_n^+\) and of anionic cobalt clusters \(Co_n^-\) in the size range \(n = 3 - 28\) and of bimetallic cobalt platinum clusters \([Co_nPt_m]^{+/-}\) in the size range \(n + m \le 8\). Dehydrogenation by cationic cobalt clusters \(Co_n^+\) is sparse, it is effective in small bimetallic clusters \([Co_nPt_m]^+ (n + m \le 3)\). Thus single platinum atoms promote benzene dehydrogenation while further cobalt atoms quench it. Dehydrogenation is ubiquitous in reactions of anionic cobalt clusters. Mixed triatomic clusters \([Co_2Pt_1]^-\) and \([Co_1Pt_2]^-\) are special in causing effective reactions and single dehydrogenation through some kind of cooperativity while \([Co_nPt_{1,2}]^- (n \ge 3)\) do not react at all. Kinetic isotope effects KIE(n) in total reaction rates are inverse and - in part - large, dehydrogenation isotope effects DIE(n) are normal. A multistep model of adsorption and stepwise dehydrogenation from the precursor adsorbate proves suitable to rationalize the found KIEs and DIEs in principle. Particular insights into the effects of charge and of cluster size are largely beyond this model. Some DFT calculations - though preliminary - lend strong support to the otherwise assumed structures and enthalpies. More insights into the cause of the found effects of charge, size and composition of both pure and mixed clusters shall arise from ongoing high level ab initio modeling (of especially the \(n + m = 3\) case for mixed clusters).The influence of the methylester group in the molecules aspartame (Asp-PheOMe) and Asp-Phe has been explored. Therefore, their protonated and deprotonated species and their complexes with alkali metal ions attached were investigated with different techniques utilizing mass spectrometry.Gas phase H-/D-exchange with \(ND_3\) has proven that in both molecules all acidic NH and OH binding motifs do exchange their hydrogen atom and that simultaneous multi exchange is present. Kinetic studies revealed that with alkali metal ions attached the speed of the first exchange step decreases with increasing ion size. The additional OH of the carboxylic COOHPhe group in Asp-Phe increases the exchange speed by a constant value. CID experiments yielded water and the protonated Asp-Phe anhydride as main fragments out of the protonated molecules, neutral Asp anhydride and \([Phe M]^+ / [PheOMe M]^+\) for \(Li^+\) and \(Na^+\) attached, and neutral aspartame / Asp-Phe and ionic \(M^+\) for \(K^+\), \(Rb^+\) and \(Cs^+\) attached. The threshold energy \(E_{CID}\), indicating ion stability, decreases with increasing ion size. For aspartame fragmentation occurs at lower \(E_{CID}\) values for complexes with \(H^+\), \(Li^+\) and \(Na^+\) than for the Asp-Phe analoga. Complexes with \(K^+\), \(Rb^+\) and \(Cs^+\) give the same \(E_{CID}\) value for aspartame and Asp-Phe. IR-MPD investigations lead to the same fragments as the CID experiments. In combination with quantum mechanical calculations a change in the preferred structure from charge-solvated, tridentate type for complexes with small alkali metal ions (\(Li^+\)) to salt-bridge type structure for large alkali metal ions (\(Cs^+\)) could be confirmed. Calculations thereby reveal nearly no structural differences between aspartame and Asp-Phe for cationized species. The deprotonation of the additional COOHPhe group in Asp-Phe is preferred against other acidic positions. A better experimental distinction between possible (calculated) structure types would arise from additional FEL IR-MPD measurements in the energy range of 600 to 1800 \(cm^{-1}\). The comparison of the \(E_{CID}\) values with calculated fragmentation energy values proves that not only for alkali metal complexes with \(K^+\), \(Rb^+\) and \(Cs^+\), but also for \(Li^+\) and \(Na^+\) the bond breaking of all metal atom bonds is part of the transition state. The lower \(E_{CID}\) values for aspartame with small cations may be explained in terms of internal energy. Aspartame is a larger molecule, possesses more internal energy and can be recognized as the larger heat bath. Less energy is needed for fragmentation, if the Phe part with the additional methylester group is involved in the fragmentation process.

Applications of carboxylic acids and their derivatives in transition metal-catalyzed cross-coupling reactions regio-selectively forming Csp3-Csp2, and Csp2-Csp2 bonds were explored in this thesis. Several important organic building blocks such as aryl acetates, diaryl acetates, imines, ketones, biaryls, styrenes and polysubstituted alkenes were successfully accessed from carboxylic acids and their derivatives by the means of C–H activation and decarboxylative cross-couplings.
An efficient and practical protocol for the synthesis of biologically important ethyl 2-arylacates through the dealkoxycarbonlative cross-coupling reaction between aryl halides and malonates was developed. Activation of the alpha-proton of alkyl esters by a copper catalyst allowed the deprotonation of esters even in the presence of mild bases, leading to a straightforward and efficient approach to alkyl alpha-diarylacetate from simple alkyl acetates and aryl halides.
The addition of a primary amine into the coupling reaction of alpha-oxocarboxylic acids and aryl halides led to an unprecedented low-temperature redox-neutral decarboxylative coupling process, providing a green and efficient method for the preparation of azomethines, in which all the three substituents can be independently varied. A minor modification of this protocol allowed us to easily access the corresponding ketones.
The decarboxylative coupling of robust aryl mesylates as well as polysubstituted alkenyl mesylates using our customized imidazolyl phosphine ligands was realized, further expanding the scope of carbon electrophiles in decarboxylative coupling reactions. Variation of the ligands led to two complementary protocols, providing the corresponding biaryls and polysubstituted olefins in high yields.
The use of a new class of pyrimidinyl phosphine ligands dramatically reduced the reaction temperatures of decarboxylative cross-coupling reactions between aromatic carboxylic acids and aryl or alkenyl triflates. The new catalyst system for the first time allowed the efficient decarboxylative biaryls synthesis at only 100 °C, representing a significant achievement in redox-neutral decarboxylative coupling reactions.

In this study, two outstanding subgroups of organic-inorganic hybrid materials have been investigated. The first part covers the design, synthesis, characterization and application of seven novel Metal Organic Frameworks (MOFs) containing functionalized biphenyl dicarboxylates as linkers. In the second part, the surface modification of the metal oxides ZrO2, TiO2 and Al2O3 using phosphonate derivates is reported.
Firstly three functionalized MOF structures; ZnBrBPDC, ZnNO2BPDC and ZnNH2BPDC were synthesised using 4,4´-biphenyldicarboxylic acid derivatives with different functional groups (-Br, -NO2, -NH2) Powder X-ray diffraction (PXRD) measurements indicated that the synthesised MOFs posses the interpenetrated IRMOF-9 structure with a cubic topology, which was also confirmed with single crystal X-ray measurements. The chemical structure of the MOF materials was further proved by solid state NMR and IR measurements. N2 adsorption measurements showed Type I isotherms for all three structures with large surface areas. TGA measurements of the evacuated samples were in good agreement with the elemental analysis data. The results proved that their thermal stability is between 325 °C - 450 °C.
Adsorption properties of these MOF structures were tested using light alkanes (CH4, C2H6, C3H8, and n-C4H10) at three different temperatures. For all adsorbents, the maximum uptakes were observed at 273 K. When the temperature was increased, the amount of the adsorbed gas decreased. All three MOFs showed strong affinities for n-butane. The lowest uptakes were observed for CH4.
The effect of functional groups on the IRMOF series was also examined by synthesizing amide functionalized biphenyl linkers. For this purpose, four different linkers containing amides with different alkyl chains (C1-C4) were synthesized and used for the synthesis of four new MOF structures ZnAcBPDC, ZnPrBPDC, ZnBuBPDC and ZnPeBPDC.
PXRD measurements of ZnAcBPDC indicated that the structure contains two different phases. PXRD patterns of ZnPrBPDC, ZnBuBPDC and ZnPeBPDC revealed non-interpenetrated structures which were further proved by single crystal X-ray measurements. The chemical structure of the MOF materials was further confirmed by X-ray spectoscopy, solid state NMR and IR measurements.
N2 adsorption measurements of the MOF structures were carried out using different activation methods. For all four MOFs, Type I isotherms were obtained. ZnAcBPDC showed the highest BET surface area. ZnAcBPDC and ZnBuBPDC were tested for their alkane, alkene and CO2 adsorption capacities.
In the second part of the work, the surface modification of three different metal oxides, ZrO2, TiO2 and Al2O3 was performed. For this purpose firstly three different fluorescent phosphonate derivatives containing thiophene units were synthesized from their halo derivatives in a four step synthesis and then used as coupling molecules for the surface modification. Nine different surfaces were obtained (38@TiO2, 39@TiO2, 40@TiO2, 38@Al2O3, 39@Al2O3, 40@Al2O3, 38@ZrO2, 39@ZrO2, 40@ZrO2).
All three modified metal oxide surfaces were characterized using elemental analysis, solid state NMR and IR spectroscopy. The BET surface areas of the materials were determined by N2 adsorption measurements. TGA was used to determine the stability of the surfaces. Maximum loadings were obtained for ZrO2 surfaces.
Due to the strong luminescence of the coupling molecules, the modified surfaces were checked for their light emission. All ZrO2 and Al2O3 surfaces showed fluorescence with exception of 40@Al2O3. On the other hand, for the modified TiO2 surfaces, no fluorescence could be observed.